In recent years, even if the raw material cost rises, it is difficult to add it to the product selling price, and then a product is required to have a lower cost. In addition, an air conditioner is also required to appeal energy saving and noise reduction as important factors of an air conditioning product. Injection molded products made of a resin material are often used in air conditioners as propeller fans adopted in many blowers of outdoor units, and turbo fans in ceiling cassette four-direction blowers of indoor units, for example. The injection molded product made of the resin material, not sheet metal, has high degree of freedom in shape and is advantageous for mass production to achieve high efficiency, low noise, and a low cost. Generally, a fan of a blower blows in the outdoor unit of an air conditioner at a rotation speed in a wide range such as from about 100 rpm to about 1000 rpm, which is calculated from such as an ambient temperature and a temperature of refrigerant in the refrigeration cycle of the air conditioner. Therefore, vibration and noise may be increased at a specific rotation speed due to resonance with a casing of the air conditioner. Increase in vibration and noise due to resonance is a serious problem for the user of the air conditioner, and therefore a rotation speed in resonance with the casing of the air conditioner is investigated in advance to devise such as a way of exerting control without using the rotation speed.
On another note, there are many cases where a plurality of outdoor units of an air conditioner, such as outdoor units of multi-split air conditioner for office buildings, are installed in bulk on the rooftop of an office building. In such cases, the outdoor units of the air conditioners are often arranged on vibration isolation racks at the time of installing the air conditioners, in order to avoid transmitting the vibration to the building structure. In addition, in Tohoku, Hokkaido, and Hokuriku districts of Japan, a rack may be made in order to install an outdoor unit of an air conditioner at a height with snow cover taken into account, for preventing the heat exchanger of the outdoor unit from being buried by snow coverage, to arrange the outdoor unit on the rack. Further, an indoor unit of an air conditioner may require hanging bolts for hanging the indoor unit to have different lengths depending on installation points due to the structure of the building at the time of installing the indoor unit. Accordingly, the natural vibration frequency in the state of the air conditioner being hung differs little by little depending on the installation conditions. In these cases, the natural vibration value obtained by integrating the outdoor unit of the air conditioner and the rack varies depending on the installation condition at the site.
Japanese Patent Application Publication No. 2010-065594 discloses a failure diagnosis apparatus of an electric blower including: a detection device that detects at least one of vibration and noise generated from an electric blower; and a controller that compares frequency components of the detected at least one of vibration and noise with the frequency components specific to the normal electric blower to detect a failure of the electric blower and to determine a failure mode.
Japanese Patent Application Publication No. 2013-234797 discloses an air conditioner including: a vibration detector that detects vibration of a blower arranged in a casing; and a controller that controls the blower based on output from the vibration detector, wherein the vibration detector is arranged on a support plate of the blower so as to detect vibration in the transverse direction of the casing.